The last universal common ancestor, or universal cenancestor is hypothesized as being at the ancestral root of all living organisms. Not the earliest or simplest living organism, and not necessarily the sole example of its type, LUCA possessed the genetic material that diverged (about 3.5 Ga) into all currently living organisms. So, the last universal common ancestor sits at the first point of divergence of any cladogram that groups living organisms according to evolutionary-genetic relationships.

A number of terms are employed to refer to the universal cenancestor – last universal ancestor (LUA), last common ancestor (LCA), or last universal common ancestor (LUCA).

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